Heavy hydrocarbon oils such as AR obtained by treating crude oil using an atmospheric distillation unit and VR obtained by further treating AR using a vacuum distillation unit contain a large amount of sulfur compounds. When these heavy hydrocarbon oils are used as a fuel without desulfurization, a large amount of sulfur compounds (SOx) are discharged into the air and the discharged sulfur causes damage to the environment. Therefore, it is necessary to reduce the amount of sulfur compounds in the heavy hydrocarbon oils.
As a result, improvements in activity and life of a hydrogenation catalyst have been studied intensively for the purpose of reducing the amount of sulfur compounds in heavy hydrocarbon oil. For example, it has been disclosed that the dispersion state of molybdenum, which is an active metal, becomes satisfactory and desulfurization performance is improved by incorporating zinc and phosphorus into an alumina carrier in an alumina-based hydrogenation catalyst (for example, refer to PTL 1).
On the other hand, heavy hydrocarbon oil is required to have improved storage stability. Hydrogenated heavy hydrocarbon oil is stored under heating to maintain fluidity until shipping in consideration of workability at the time of shipping. In addition, the oil may be stored for a long period of time after the oil is shipped as a product before use. Therefore, depending on the thermal history and the atmosphere at the time of storage, sediment is produced while the oil is stored and this sediment may cause plugging of a filter or damage to a pump.
There are several reasons why sediment is produced, one of these being due to the stability of asphaltene contained in heavy hydrocarbon oil. When asphaltene is surrounded by resin, the asphaltene is dispersed in heavy hydrocarbon oil without producing sediment. However, when resin is dissociated from asphaltene by hydrogenation and the balance between the asphaltene and the resin collapses, the asphaltene easily appears as sediment.